First you need to get the safe ending. Choose doors 5, 8, and 6. Be sure to click on the safe in the door 5 room after solving the puzzles! This is the bad ending that is required before you can see the True Ending.

How to get true ending after that? ...I am not gonna tell you everything!

999 is, hands down, the bets visual novel I have ever played! (Next to Clannad... which is kinda awkward.)
The atmosphere, the music, the characters... it was so amazing how they tied everything together, and just totally messed with your head!

I haven't played the sequel yet, but I've heard a lot of people don't like it... To be honest, I have no interest in sequels to games that aren't meant to have one.

AHHH!!!!! *FANGIRLING RIGHT NOW* I played this game a year ago when I had a GameFly account and let me say that this game easily scared me because I saw a review for it in a magazine but I didn't know it was rated M. All I saw was that it was an anime visual novel type game for the DS which is pretty rare (to me at least). But once I played it, it has become one of my favorite DS games of all time. If you haven't played it yet, I suggest you should! You won't regret it! (: